Contactless snap-action limit switch



Nov. 21, 1961 L PIERCE ET AL CONTACTLESS SNAP-ACTION LIMIT SWITCH FiledNov. 18, 1958 Fig. I.

Fig.6.

INVENTORS Lawrence Pierce 8 Marshall R White. BY

WlTNESSES: @W RKG' ATTORNEY United States Patent This invention relatesto limit switches and more particularly to limit switches utilizingcontactless static magnetic elements.

There are many limit switches known in the prior art but such prior artswitches include movable contacts that present a maintenance problem,since the reliability and useful life of movable contacts fall short ofthe standards of operationrequired in many industrial applications.

One object of this invention is the provisionof movable and stationarymagnetic elements for producing a pulse of magnetization in a magneticcircuit which is effective to produce a switching action in a circuit.

It is a broader object of this inventionto providemagnetically actuatedcontactless limit switches.

The objects recited are merely illustrative. Other objects andadvantages will become more apparent from a study of the followingspecification and drawings, in which: i

FIGURE 1 is a plan view, with the casing removed, of a limit switchembodying the invention;

FIG. 2 is a longitudinal sectional. view of the showing made in'FlG. 1;

FIGS. 3, 4 and 5 show some elements in detail; and- FIG. 6 is adiagrammatic view of a basic circuit for a switching system with whichthe mechanical elements of this invention are used.

FIGS. 1 and 2 together showthe complete limit switch.

A molded assembly 12 carries. an encapsulated saturable reactor. Theassembly is rigidly bolted to. the base 6. In

FIG. 2 the cover 1 is shown in position. The cover has the conduitopening at the left through which the leads are passechfor connection tothe terminals 7. and 7 for.

leakage between the magnets 2 and 3, rigidly mounted on.

shaft B. The length of shaft B is slightly greater than the width of thepedestal P.

The magnet 2 is securely clamped to the left, end of the shaft B bymeans of the brass screw A. Magnet 3 is similarly clamped on the rightend of; shaft B by means of" brass screw E.

The structure of screw E is, however, considerably different than screwA. Screw E is somewhat elongated and has a shoulder at itsmid regionwith theregion to the right of the shoulder-being an enlargedcylindrical portion to form a bearing stud between the head ofthe screwand the shoulder for the brass beveled pinion 5 and; the

magnet 4 secured to the pinion 5. A pair of brass spacing washers, oneto fit over the threaded, end Cfscrew E and one to fit over thecylindrical portion, are disposed between the magnets 3. and 4. Whenthescrew ,E is tightened into the brass sleeve shaft Bthe magnets 2 and 3are rigidlyclamped on shaft B to rotate, as a unit, but the bevel gear 5and. magnet 4, secured to gear 5. by bracket 21, are free to rotate onscrew E between the 3,010,039 Patented Nov. 21, 1961 screw head and theright-hand spacing washers disposed between magnets 3 and 4.

end being disposed, as seenin FlG. 2, in front of the pin 15 projectingrigidly vertically from the base 6, and the other end. being disposedbehind both pins 14 and 15. The bracket 13 has the construction shown inFIG. 4 and thus. must rotate with shaft 19.

A lever-18 is adjustably secured to the lower end of the shaft 19. Theouter end of-the lever carries a roller which engages a suitable dog on.a movable part of a machine requiring a limit switch.

The magnet 4 is secured to the bracket 21 as shown in FIG. 3 and theback of the bracket, in the assembled relation, is brazed to the beveledpinion 5.

A non-magnetic stop 22, constructed as shown in FIG. 5, is boltedbymeans of a non-magnetic bolt to the base 6, as shown inFIG. 1. This.stop prevents the magnets 2 and 3 from rotating clockwisewhen viewedfrom, the left. When the lever 18 is not actuated, the springlti sobiases the parts that the south pole of magnet 4, is, whenviewed fromthe-left, about 45 degrees in a counterclockwise direction from thevertical. Magnet 4 thus tends to rotate magnet 3 clockwise, but the stop22 prevents such rotation. Magnets 2 and 3 are thus normally inavertical position with their north polesat the top.

In the showings of both FIGS. 1 and 2, the lever 18 is shown as havingbeen actuated by the dog on the machine from the normal position of themagnets hereinbefore mentioned to just prior to the triggering position,This movement was for lever 18 from above the paper into the paper, asseen in FIG. 2, or from some clockwise position to the counterclockwiseposition shown in FIG. 1. As this movement continues, the magnets firstline up as shown in both FIGS. 1 and 2, and a moment later as the northpole of magnet 4 moves-out of the paper, the north poleof magnet? isrepelled, and both magnets 2 and 3 move counterclockwise, as seen fronthe left in FIG. 2, with a snap action. The reactance value of thereactor is thus changed from an unsaturated condition to a saturatedcondition, and the switching operation is effected.

When the dog on the machine, not shown, releases the lever 18 the spring16 rapidly restores the lever 18 to its full; clockwise position (belowthe position shown in FIG. 1). As the lever 18 makesthis movement, themagnet 4 moves counterclockwise, and as it moves past its horizontalposition, the magnets 2 and 3 snap back to the position shown.

When the Alnico magnet 2 is in a vertical position,

- as. shown, then the major portion of its flux is shunted actorimpedance will thus be low. This change in reactor, i-inpedanceis hereused to operate the limit switch circuit shown in FIG. 6. i

This limit switch circuit comprises four rectifying elements D1, D2, D3and D4, two resistors R1 and R2, and a contactless saturable reactortype limit switch comprism ing the switch assembly shown in FIGS. 1 and2. As

above described, the switch among other elements comprises aperrnanentmagnet 2 which is actuated by a quick action, as explained hereinaboveto vary the saturation of the reactor core.

When the core 9 of the reactor is saturated only a small part of theapplied voltage is absorbed by the reactor and most of the voltageappears at the output terminals of the switching system. When the coreis unsaturated, the inductance, and hence the impedance, is very highand most of the applied voltage is absorbed by the reactor, andsubstantially none appears at the output terminals of the switchingsystem.

As shown in FIG. 6, an alternating-current voltage of one phase, orinstant polarity is applied to input terminal 113. Analternating-current voltage of a different phase of oppositeinstantaneous polarity 6 is applied to input terminal 114. An outputterminal 130 may be con nected to a magnetic logic element of a controlboard. This logic element is set to select only 6 phase voltages. Anoutput terminal 14 may be connected to a magnetic logic element which isset to select only phase voltages. Both magnetic logic elements areconnected to a common conductor C. The resistor R1 is connected to a DC.voltage and resistor R2 is connected to a D.C. qb voltage.

As previously explained, when the limit switch reactor core 9 isunsaturated, the reactor has a high impedance which causes the 0 andoutputs to go to zero. When the p input voltage is considered as beingcurrent flows through the rectifier D3 to provide a output of 13.However, this output signal is of no importance since the logic elementLE6 which it is feeding is set to select only 9 voltages. There will beno 5 output at 14 because most of the applied voltage is absorbed by thereactor. The reactor magnetizing current is passed by the D2, R2, D.C.combination to hold the output at 14 at zero. The positive side of DC.qb voltage is connected to the common conductor C. When the A.C. voltageis considered as being the A.C. 6 voltage is and current is preventedfrom flowing by the rectifier D4. Therefore, there is no 0 output signalat this time.

When the A.C. 6 voltage is considered as being there will be a 0 outputsignal at 14. This signal is of no importance since the logic element LEwhich it is feeding is set to select only s signals. There is no 0output signal at 130 because the applied voltage is absorbed by thereactor. The magnetizing current for the reactor is passed by D1, R1,D.C. combination, thereby holding the output at 130 at zero. When theA.C. voltage is the A.C. voltage is and current is prevented fromflowing by the rectifier D3.

It should be noted that the reactor core is reset every half cycle. Thisis done first by one of the alternatingcurrent sources and then by theother. if the reactor core is not reset, the impedance would be smalland the limit switch would be ineffective.

As previously explained, when the reactor core 9 is saturated by themagnet 2, there is only a small voltage drop across the reactor.Therefore, the A.C. voltage will appear at the output terminal 14 andthe A.C. voltage will appear at the output terminal 130. Thus, theswitching system may be used to control magnetic logic elements and thusload units. With both 0 and 5 outputs, it is possible to drive oroperate twice as many logic elements as was previously possible. Also,it is possible to separately operate the 0 and o logic elements.

Since changes may be made in the above-described construction anddifferent embodiments of the invention may be made without departingfrom the spirit and scope thereof, it is intended that all the mattercontained in the foregoing description or shown in the accompanyingdrawing shall be interpreted as illustrative and not in a limitingsense.

'We claim is our invention:

1.. In a l mit switch actuator, in combination, a base,

bearing means on the base, a first shaft disposed for rotation in saidbearing means, a second shaft, a crankarm. mechanically coupled to saidsecond shaft, said crank-arm being biased to a given position on saidbase, a permanent magnet rigidly coupled to one end of the first shaftand having its poles disposed on opposite sides of the first shaft, asecond permanent magnet operatively coupled to the second shaft anddisposed for free rotation on an axis coincident with the axis of thefirst shaft and being disposed in close proximity to the first magnetand in facing relation thereto, stop means disposed on the base andpositioned to limit the movement of the first magnet through an anglethat is a fraction of one complete turn, said stop being so positionedthat the repulsion force of the like poles of the magnets, when thelever is in its biased position, forces the first magnet with asnap-action to one position with respect to the stop, switching meanshaving two positions, said switching means being caused to move to oneposition with a snap-action upon movement of the first magnet to oneposition and, when the lever is rotated through a given angle from itsbiased position, force the first magnet, with a snap-action as the leveris being moved, to a second position with respect to the stop, saidswitching means being caused to move to its second position with asnapaction upon movement of the first magnet to its second position.

2. In a limit switch actuator, in combination, a base, bearing means onthe base, a shaft disposed for rotation in said bearing means, acrank-arm mechanically coupled to one end of said shaft, said crank-armbeing biased to a given position on said base, a bevel gear connected tothe other end of of said shaft, second bearing means on said base havinga bearing axis normal to the axis of the shaft in the first mentionedbearing means, a shaft in the second bearing means, a bevel piniondisposed for rotation on one end of the second shaft and meshing withthe bevel gear, a firs-t permanent magnet rigidly coupled to the bevelpinion and having its poles disposed on opposite sides of the secondshaft, a second permanent magnet secured to the second shaft disposedfor free rotation with the second shaft and being disposed in closeproximity to the first permanent magnet and in facing relation thereto,stop means disposed on the base and positioned to limit the movement ofthe second magnet through an angle that is a fraction of one completeturn, said stop being so positioned that the repulsion force of the likepoles of the magnets, when, the lever is in its biased position, forcesthe second magnet to one position with respect to the stop, and, a thirdmagnet rigidly coupled to the second magnet but spaced from the secondmagnet to be substantially unaffected by leakage flux from the secondmagnet, and inductive contactless switching means caused to operate bythe snap-action movement of the third magnet.

3. In a limit switch actuator, in combination, a base, bearing means onthe base, a shaft disposed for rotation in said bearing means, acrank-arm mechanically coupled to one end of said shaft, said crank-armbeing biased to a given position on said base, a bevel gear connected tothe other end of said shaft, second bearing means on said base having abearing axis normal to the axis of the shaft in the first mentionedbearing means,

a shaft in the second bearing means, a bevel pinion disposed forrotation on one end of the second shaft and meshing with the bevel gear,a permanent magnet rigidly coupled to the bevel pinion and having itspoles disposed on opposite sides of the second shaft, a second permanentmagnet secured to the second shaft and disposed for free rotation withthe second shaft and being disposed in close proximity to the firstmagnet and in facing relation thereto, stop means disposed on the baseand positioned to limit the movement of the second magnet through anangle that is a fraction of one complete turn, said stop being sopositioned that the repulsion 5 6 force of the like poles of themagnets, when the lever position causing a rapid change oi flux in saidcore to is in its biased position, forces the second magnet to oneeffect a switching operation.

position with respect to the stop, and, a third magnet rigidly coupledto the second magnet but spaced from the Refetences Cited in the me ofpatent second magnet to be substantially unaffected by leakage 5 UNITEDSTATES PATENTS flux from the second magnet, a core composed of mag-2,378,129 Chambers June 12, 1945 netic material, a coil disposed on thecore, pole pieces at 2,414,688 Chambers Jan. 21, 1947 Opposite ends ofthe core, said third magnet when moved 2,471,947 Giannini May 31, 1949by snap-action from its unactuated position to its actuated 2,856,591White Oct. 14, 1958

